Prussian blue analogs with an open framework are ideal cathodes for Na‐ion batteries. A superior high‐rate and highly stable monoclinic nickel hexacyanoferrate (NiHCF‐3) is synthesized via a facile one‐step crystallization‐controlled co‐precipitation method. It gives a high specific capacity of 85.7 mAh g−1, nearly to its theoretical value. It also exhibits an excellent rate capability with a high capacity retention ratio of 78% at 50 C and a stable cycling performance over 1200 cycles. Through the ex situ X‐ray diffraction and pair distribution function measurements, it is found that the monoclinic structure with distorted framework is greatly related to the high Na content. The electronic structure studies by density functional theory (DFT) calculation demonstrate that NiHCF‐3 deformation promotes the framework conductivity and improves the electrochemical activity of Fe, which results in an ultrahigh‐rate performance of monoclinic phase. Furthermore, the high‐quality monoclinic (NiHCF‐3) exhibits excellent compatibility with both hard carbon and NaTi2(PO4)3 anodes in full cells, which shows great prospects for the application in the large‐scale energy storage systems.

In situ monitoring of the interfacial processes in working all-solid-state lithium–sulfur batteries provides deep insights into the degradation mechanisms and temperature dependence.

Li + -conductive ceramic oxide electrolytes, such as garnetstructured Li 7 La 3 Zr 2 O 12, have been considered as promising candidates for realizing the next-generation solid-state Li-metal batteries with high energy density. Practically, the ceramic pellets sintered at elevated temperatures are often provided with high stiffness yet low fracture toughness, making them too brittle for the manufacture of thin-film electrolytes and straininvolved operation of solid-state batteries. The ceramic powder, though provided with ductility, does not yield satisfactorily high Li + conductivity due to poor ion conduction at the boundaries of ceramic particles. Here we show, with solid-state nuclear magnetic resonance, that a uniform conjugated polymer nanocoating formed on the surface of ceramic oxide particles builds pathways for Li + conduction between adjacent particles in the unsintered ceramics. A tapecasted thin-film electrolyte (thickness: <10 μm), prepared from the polymer-coated ceramic particles, exhibits sufficient ionic conductivity, a high Li + transference number, and a broad electrochemical window to enable stable cycling of symmetric Li/Li cells and all-solid-state rechargeable Li-metal cells.